The bee mite Varroa destructor is one of the biggest threats for apiculture world wide. The ectoparasite was introduced into Europe from Asia in the 1970s where it shifted from its natural host, the Eastern honeybee Apis cerana, to the European honeybee Apis mellifera. Apis mellifera turned out to be particularly sensitive to the ectoparasite such that Varroa destructor successfully spread throughout the entire world within a few decades. The only country, which was so far spared from Varroa destructor, is Australia. Consequently, hardly any bee colonies exist nowadays, which are free of Varroa destructor. 
Varroa destructor infestations significantly afflict honeybee colonies causing losses of up to 30% during hibernation. Without treatment, honeybee colonies infested by Varroa destructor die within two to three years. Overall, Varroa destructor is believed to considerably contribute to the dying of bee colonies, which is observed throughout the entire globe.
To control Varroa mite infestation primarily liquid compositions of various chemicals are used, including synthetic acaricides, organic acids and essential oils. Common synthetic acaricides are based on organophosphate coumaphos, pyrethroides, tau-fluvalinate, flumethrin or amitraz. Most of these pesticides are easy to apply and convenient in practice, because they do not required refined knowledge of the mites' biology. They posses, however, considerable disadvantages, since most of the synthetic acaricides are lipophilic substances and are therefore absorbed by the bees' wax where they accumulate over time. This can harm the bees, which are continuously exposed to increasing amounts of multiple compounds stored in the wax. Moreover, the chemicals can pollute the honey and other bee products, as already observed with residues of synthetic acaricides exceeding the European Union maximum limit in various honeybee products. Additionally and most importantly, synthetic acaricides were found to create resistances of the Varroa mites, leading to unrecognized failure of control in the field and serious damage of beekeeping. Organic acids and essential oils used for Varroa control include formic acid, oxalic acid, lactic acid and thymol. Formic acid is the most extensively used, since it is the only acaricide, which is able to kill mites within sealed brood cells. Organic acids and essential oils, in general, have a low risk of accumulating in bee products. They show, however, substantial disadvantages in their handling and application. Lactic acid and oxalic acid, for example, have to be applied under broodless conditions and thus are only suitable for colonies kept in regions with a brood stop during winter. In addition, the efficiency of some compounds depends on the climatic conditions outside as well as inside the bee hive, e.g. the evaporation pressure within the colony, such that the efficiency of these acaricides is difficult to control. In general, for most organic acids and essential oils, the range between their efficiency regarding parasite extinction and their toxicity for the host is particularly narrow, such that the effects of these substances are often variable and unreliable.
Therefore, an efficient treatment of Varroa infestation is needed which allows an easy application and handling while preventing undesired side effects on bee colonies and their products.